Various thin films and thick films have been conventionally formed by a CVD method, etc. in production processes for thin film devices in semiconductor productions, etc. In forming such thin films for semiconductors, a thin film material unfavorably attaches to parts other than a target for forming films, said parts being the inner wall of a reactor, jigs for supporting the target, pipes and the like. Such a deposit induces contamination of fine particles into semiconductor products. As a result, it is difficult to produce a high quality thin film, and the contamination occasionally brings about lowering in the yield of products. Therefore, it is necessary to remove such a deposit at any time. Usually, the deposit has been removed with hands, cleaning gases and the like.
In semiconductors, etc., thin film materials have been partly removed by the use of gas etching in order to form circuit patterns of the various thin film materials for constituting semiconductor circuits.
The basic properties required for these gases are a high cleaning rate for the cleaning gas and a high etching rate to a target and high selectivity for the etching gas. Additionally, both of the gases, from which harmful gases for environment are not generated preferably, are desired to have a low load for global environment.
Conventionally, in the step of producing semiconductor devices, large amounts of fluorine gases, such as CF4, C2F6, SF6 and NF3, have been used as a gas for cleaning such deposits or as a gas for etching thin films.
These fluorine gases, however, are stable compounds having long atmospheric lifetime. The fluorine gases have a problem in that after cleaning or etching, it is difficult to treat un-decomposed gases and the cost for the treatment is high. The fluorine gases, further, have a very higher global warming potential (100-year integrated global warming potential) as compared with CO2. For example, the global warming potential of CF4 is 5,700 times, that of C2F6 is 11,900 times, that of SF6 is 22,200 times and that of NF3 is 10,800 times higher than that of CO2, so that they have a fear of adverse impacts on the environment. Consequently, the development of alternative gases having a low global warming potential and excellent capability of cleaning off a deposit containing silicon in semiconductors, or excellent capability of etching a film containing silicon has been desired.
Further, even if the gases used have themselves no much influence on the environment, by decomposing these gases after cleaning or etching, gases having a long atmospheric life, such as CF4, which are harmful to the environment, may be generated. Therefore, the development of alternative gases which have no harmful influence on the environment even after the decomposition has been desired.